1. Field of the Invention
This invention relates to fasteners for machine parts and more particularly to a method for facilitating the removal of sheared-off machine screw and bolt shanks from a machine part.
2. Brief Description of the Prior Art
The common problem of removing sheared-off machine parts such as engine blocks, metal castings and the like is well known to practically all persons concerned with machine maintenance and repair. Sheared-off machine screw and bolt shanks often occur as a consequence of extraordinary wear or abuse of a machine during use or transportation or as a result of over-torquing the fastener with the consequent shearing off of the head portion during inserting or removal. Where the environment includes high temperature or moisture conditions or both "freezing" of the threads commonly occurs due to formation of rust tending to lock the fastener in its bore, leading to such failures and exacerbating the removal problem. While coating the threads with lubricant has been practiced in the past, the quality of lubricant is usually inadequate to prevent drying out or other dissipation thereof over the course of time, such that such freeze-ups will still occur.
It is also well known that the removal of the sheared-off bolt or screw shank often presents an extremely difficult problem. One approach to the removal problem is to drill out the sheared-off shank portion. This technique often results in damage to the tapped hole within which the sheared-off shank resides with the consequential need for enlarging and retapping the hole. Other techniques are also somewhat difficult and are either destructive to the fastened machine part or substantially time consuming, or both. Accordingly, there exists a need for a solution to the problem of removing sheared-off screw and bolt shanks in an expeditious and non-destructive fashion, particularly in those environments tending to produce freeze-up of the fastener.